This invention relates generally to packs for testing the efficacy of a steam sterilization system. More specifically, the invention relates to a test pack which can be used with either a biological indicator or a chemical indicator to determine the efficacy of the sterilization system. The present invention is particularly, although not exclusively, useful for the testing of sterilizing equipment used for the sterilization of hospital and medical equipment.
The sterilization of medical equipment by exposure to steam is typically accomplished by using an autoclave. Normally, the equipment to be sterilized is placed within the autoclave and a vacuum may or may not be drawn depending on the particular procedure being followed. The sterilization medium, steam, is then introduced into the autoclave to permeate the equipment and sterilize it.
According to standard hospital procedures, steam sterilization equipment needs to be periodically tested to insure the sterilization process is efficacious. Such a test preferably requires subjecting spores of living microorganisms to the sterilization cycle and subsequently observing whether they have remained viable. To insure that the sterilization process is efficacious by sufficiently challenging the sterilization equipment, these spores need to be protected as well or better than they would ordinarily be protected if lodged in the most inaccessible recesses of the hospital packs to be sterilized.
Several procedures have been proposed to test the efficacy of steam sterilization equipment. Typical of these, and perhaps the best known and most widely used, is the procedure recently published by the Association for the Advancement of Medical Instrumentation (A.A.M.I.) as A.A.M.I. SSSA 1988 ("Good Hospital Practice: Steam Sterilization and Sterility Assurance"). According to the A.A.M.I. recommended practice, 16 freshly laundered all-cotton towels are folded by hospital personnel and stacked to construct a test pack into which a biological indicator is imbedded. This pack is then subjected to the sterilization cycle.
Although apparently efficacious for its intended purpose, the construction of a test pack according to the A.A.M.I. procedure is labor intensive and the resulting pack is relatively bulky. In light of these limitations, the present invention satisfies the need for a pre-assembled composite sterilization test pack which is convenient to handle and which will challenge steam sterilization equipment to the same degree as the 16 towel test pack. This is accomplished by surrounding a biological indicator with material which will delay steam entry to the indicator and provide the indicator with a degree of thermal insulation.
U.S. Pat. No. 4,636,472 discloses such a pre-assembled composite sterilization test pack which employs a combination of porous and non-porous materials in order to effect the desired interplay of steam entry to the indicator and degree of thermal insulation. The patented disposable sterilization test pack includes a base pad comprising a plurality of porous sheets having holes cut therethrough which are stacked to align the holes and form a cavity for receiving a sterilization indicator therein. A top pad and a bottom pad, each typically comprised of a plurality of gas permeable porous sheets, are respectively placed against the top and bottom surfaces of the base pad to confine the indicator within the cavity and help inhibit the flow of gas to and from the cavity. A gas impermeable layer is disposed against the top pad on its surface which is opposite from the base pad to further inhibit gas flow to and from the cavity by preventing the passage of gas into and out of the test pack wherever the impermeable layer is in contact with the porous material of the top pad.
When subjected to a sterilization cycle, the sterilization indicator (e.g., a biological or chemical indicator), positioned in the cavity of the test pack's base pad, will react according to the efficacy of the sterilization cycle. The entire stack of layers can be covered with a CSR (central supply room) overwrap material and held together with a tape having an indicator ink imprinted thereon to show when a pack has been subjected to a sterilization process.
The patented test pack has not proven to be entirely satisfactory in use. First, it was designed to simulate a proposed 14 towel test pack which was never adopted as an A.A.M.I. standard, and thus it is not suitable as a simulation of the more stringent 16 towel test pack. Second, the use of a gas impermeable layer substantially precludes gas flow to and from the cavity through a major surface (that is, the top) of the test pack and thereby emphasizes the flow of gas to and from the cavity along the edges and intermediate the pads (or intermediate the several sheets forming the pads) of the test pack. This is especially true in the preferred embodiments wherein there is also a gas impermeable layer disposed against the bottom pad. The resultant emphasis on gas flow along the edges of the test pack and intermediate the pads thereof makes the efficacy of the pack highly sensitive to the degree of tightness with which the overwrap material is applied thereto, by affecting the ability of the gas blocked by the gas impermeable layer to nonetheless reach the cavity by passage within the test pack intermediate the overwrap material and the sides of the stack and then intermediate the adjacent faces of the more permeable sheets of the stack.
Accordingly, it is an object of the present invention to provide a pre-assembled sterilization test pack which simulates the 16 towel test pack and tests the efficacy of steam sterilization biological equipment by challenging the accessibility of steam to the indicator and providing a requisite level of insulation for the indicator.
Another object provides such a test pack which can be easily altered to change sterilization indicators according to the needs and desires of the operator.
Still another object is to provide such a pre-assembled test pack which is small, compact, easily handled by hospital personnel, convenient to use, standardized, cost effective and easily manufactured.
It is also an object of the present invention to provide such a test pack which is not overly sensitive to the tightness of a wrapping or box about the stack.
It is a further object to provide such a test pack which uses a gas-inhibiting tray to inhibit the passage of gas into and out of one surface of the test pack and to control the passage of gas into and out of the edges of the test pack.